Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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The sensitivity of wet and dry tropical forests to climate change in Bolivia
Seiler, C. ; Hutjes, R.W.A. ; Kruijt, B. ; Hickler, T. - \ 2015
Journal of Geophysical Research: Biogeosciences 120 (2015)3. - ISSN 2169-8953 - p. 399 - 413.
global vegetation models - soil respiration - terrestrial biosphere - plant geography - carbon-dioxide - amazon dieback - rain-forest - dynamics - water - temperature
Bolivia's forests contribute to the global carbon and water cycle, as well as to global biodiversity. The survival of these forests may be at risk due to climate change. To explore the associated mechanisms and uncertainties, a regionally adapted dynamic vegetation model was implemented for the Bolivian case, and forced with two contrasting climate change projections. Changes in carbon stocks and fluxes were evaluated, factoring out the individual contributions of atmospheric carbon dioxide ([CO2]), temperature, and precipitation. Impacts ranged from a strong increase to a severe loss of vegetation carbon (cv), depending on differences in climate projections, as well as the physiological response to rising [CO2]. The loss of cv simulated for an extremely dry projection was primarily driven by a reduction in gross primary productivity, and secondarily by enhanced emissions from fires and autotrophic respiration. In the wet forest, less precipitation and higher temperatures equally reduced cv, while in the dry forest, the impact of precipitation was dominating. The temperature-related reduction of cv was mainly due to a decrease in photosynthesis and only to lesser extent because of more autotrophic respiration and less stomatal conductance as a response to an increasing atmospheric evaporative demand. Under an extremely dry projection, tropical dry forests were simulated to virtually disappear, regardless of the potential fertilizing effect of rising [CO2]. This suggests a higher risk for forest loss along the drier southern fringe of the Amazon if annual precipitation will decrease substantially.
Field Evaluation of a Push-Pull System to Reduce Malaria Transmission
Menger, D.J. ; Omusula, P. ; Holdinga, M.R. ; Homan, T. ; Carreira, A.S. ; Vandendaele, P. ; Derycke, J.L. ; Mweresa, C.K. ; Mukabana, W.R. ; Loon, J.J.A. van; Takken, W. - \ 2015
PLoS One 10 (2015)4. - ISSN 1932-6203 - 20 p.
mosquito anopheles-gambiae - lasting insecticidal nets - polymerase-chain-reaction - spatial repellency - carbon-dioxide - trap catches - house entry - funestus - vectors - attractants
Malaria continues to place a disease burden on millions of people throughout the tropics, especially in sub-Saharan Africa. Although efforts to control mosquito populations and reduce human-vector contact, such as long-lasting insecticidal nets and indoor residual spraying, have led to significant decreases in malaria incidence, further progress is now threatened by the widespread development of physiological and behavioural insecticide-resistance as well as changes in the composition of vector populations. A mosquito-directed push-pull system based on the simultaneous use of attractive and repellent volatiles offers a complementary tool to existing vector-control methods. In this study, the combination of a trap baited with a five-compound attractant and a strip of net-fabric impregnated with micro-encapsulated repellent and placed in the eaves of houses, was tested in a malaria-endemic village in western Kenya. Using the repellent delta-undecalactone, mosquito house entry was reduced by more than 50%, while the traps caught high numbers of outdoor flying mosquitoes. Model simulations predict that, assuming area-wide coverage, the addition of such a push-pull system to existing prevention efforts will result in up to 20-fold reductions in the entomological inoculation rate. Reductions of such magnitude are also predicted when mosquitoes exhibit a high resistance against insecticides. We conclude that a push-pull system based on non-toxic volatiles provides an important addition to existing strategies for malaria prevention.
Mosquito host preferences affect their response to synthetic and natural odour blends
Busula, A.O. ; Takken, W. ; Loy, D.E. ; Hahn, B.H. ; Mukabana, W.R. ; Verhulst, N.O. - \ 2015
Malaria Journal 14 (2015). - ISSN 1475-2875 - 9 p.
polymerase-chain-reaction - vector anopheles-gambiae - rice irrigation scheme - sensu-stricto diptera - human skin microbiota - treated bed nets - carbon-dioxide - western kenya - plasmodium-falciparum - semifield conditions
Background The anthropophilic malaria mosquito Anopheles gambiae sensu stricto (hereafter termed Anopheles gambiae) primarily takes blood meals from humans, whereas its close sibling Anopheles arabiensis is more opportunistic. Previous studies have identified several compounds that play a critical role in the odour-mediated behaviour of An. gambiae. This study determined the effect of natural and synthetic odour blends on mosquitoes with different host preferences to better understand the host-seeking behaviour of mosquitoes and the potential of synthetic odour blends for standardized monitoring. Methods Odour blends were initially tested for their attractiveness to An. gambiae and An. arabiensis in a semi-field system with MM-X traps baited with natural and synthetic odours. Natural host odours were collected from humans, cows and chickens. The synthetic odour blends consisted of three or five previously identified compounds released with carbon dioxide. These studies were continued under natural conditions where odour blends were tested outdoors to determine their effect on species with different host preferences. Results In the semi-field experiments, human odour attracted significantly higher numbers of both mosquito species. However, An. arabiensis was also attracted to cow and chicken odours, which confirms its opportunistic behaviour. A five-component synthetic blend was highly attractive to both mosquito species. In the field, the synthetic odour blend caught significantly more An. funestus than traps baited with human odour, while no difference was found for An. arabiensis. Catches of An. arabiensis and Culex spp. contained large numbers of blood-fed mosquitoes, mostly from cows, which indicates that these mosquitoes had fed outdoors. Conclusions Different odour baits elicit varying responses among mosquito species. Synthetic odour blends are highly effective for trapping mosquitoes; however, not all mosquitoes respond equally to the same odour blend. Combining fermenting molasses with synthetic blends in a trap represents the most effective tool to catch blood-fed mosquitoes outside houses, which is essential for understanding outdoor malaria transmission.
Simulating the reactions of CO2 in aqueous monoethanolamine solution by Reaction Ensemble Monte Carlo using the Continuous Fractional Component method
Balaji, S.P. ; Gangarapu, S. ; Ramdin, M. ; Torres-Knoop, A. ; Zuilhof, H. ; Goetheer, E. ; Dubbeldam, D. ; Vlugt, T. - \ 2015
Journal of Chemical Theory and Computation 11 (2015)6. - ISSN 1549-9618 - p. 2661 - 2669.
chemical-reaction equilibria - sterically hindered amines - aerosol based emission - carbon-dioxide - molecular simulation - computer-simulation - phase-equilibria - capture - system - performance
Molecular simulations were used to compute the equilibrium concentrations of the different species in CO2/monoethanolamine solutions for different CO2 loadings. Simulations were performed in the Reaction Ensemble using the continuous fractional component Monte Carlo method at temperatures of 293, 333, and 353 K. The resulting computed equilibrium concentrations are in excellent agreement with experimental data. The effect of different reaction pathways was investigated. For a complete understanding of the equilibrium speciation, it is essential to take all elementary reactions into account because considering only the overall reaction of CO2 with MEA is insufficient. The effects of electrostatics and intermolecular van der Waals interactions were also studied, clearly showing that solvation of reactants and products is essential for the reaction. The Reaction Ensemble Monte Carlo using the continuous fractional component method opens the possibility of investigating the effects of the solvent on CO2 chemisorption by eliminating the need to study different reaction pathways and concentrate only on the thermodynamics of the system.
Emissions of particulate matter from animal houses in the Netherlands
Winkel, A. ; Mosquera Losada, J. ; Groot Koerkamp, P.W.G. ; Ogink, N.W.M. ; Aarnink, A.J.A. - \ 2015
Atmospheric Environment 111 (2015). - ISSN 1352-2310 - p. 202 - 212.
livestock buildings - northern europe - carbon-dioxide - aerial pollutants - ventilation flow - broiler activity - air-pollution - dust - balance - health
In the Netherlands, emissions from animal houses represent a major source of ambient particulate matter (PM). The objective of the present paper was to provide accurate and up to date concentrations and emission rates of PM10 and PM2.5 for commonly used animal housing systems, under representative inside and outside climate conditions and ventilation rates. We set up a national survey which covered 13 housing systems for poultry, pigs, and dairy cattle, and included 36 farms. In total, 202 24-h measurements were carried out, which included concentrations of inhalable PM, PM10, PM2.5, and CO2, ventilation rate, temperature, and relative humidity. On an animal basis, geometric mean emission rates of PM10 ranged from 2.2 to 12.0 mg h-1 in poultry and from 7.3 to 22.5 mg h-1 in pigs. The mean PM10 emission rate in dairy cattle was 8.5 mg h-1. Geometric mean emission rates of PM2.5 ranged from 0.11 to 2.41 mg h-1 in poultry and from 0.21 to 1.56 mg h-1 in pigs. The mean PM2.5 emission rate in dairy cattle was 1.65 mg h-1. Emissions are also reported per Livestock Unit and Heat Production Unit. PM emission rates increased exponentially with increasing age in broilers and turkeys and increased linearly with increasing age in weaners and fatteners. In laying hens, broiler breeders, sows, and dairy cattle, emission levels were variable throughout the year.
The uncertain climate footprint of wetlands under human pressure
Petrescu, A.J. ; Lohila, A. ; Tuovinen, J.P. ; Baldocchi, D.D. ; Desai, A.R. ; Veenendaal, E.M. ; Schrier-Uijl, A. - \ 2015
Proceedings of the National Academy of Sciences of the United States of America 112 (2015)15. - ISSN 0027-8424 - p. 4594 - 4599.
methane emissions - carbon-dioxide - peatlands - ecosystem - fluxes - variability - dynamics - drainage - balance - cycle
Significant climate risks are associated with a positive carbon–temperature feedback in northern latitude carbon-rich ecosystems, making an accurate analysis of human impacts on the net greenhouse gas balance of wetlands a priority. Here, we provide a coherent assessment of the climate footprint of a network of wetland sites based on simultaneous and quasi-continuous ecosystem observations of CO2 and CH4 fluxes. Experimental areas are located both in natural and in managed wetlands and cover a wide range of climatic regions, ecosystem types, and management practices. Based on direct observations we predict that sustained CH4 emissions in natural ecosystems are in the long term (i.e., several centuries) typically offset by CO2 uptake, although with large spatiotemporal variability. Using a space-for-time analogy across ecological and climatic gradients, we represent the chronosequence from natural to managed conditions to quantify the “cost” of CH4 emissions for the benefit of net carbon sequestration. With a sustained pulse–response radiative forcing model, we found a significant increase in atmospheric forcing due to land management, in particular for wetland converted to cropland. Our results quantify the role of human activities on the climate footprint of northern wetlands and call for development of active mitigation strategies for managed wetlands and new guidelines of the Intergovernmental Panel on Climate Change (IPCC) accounting for both sustained CH4 emissions and cumulative CO2 exchange.
Rain events decrease boreal peatland net CO2 uptake through reduced light availability
Nijp, J.J. ; Limpens, J. ; Metselaar, K. ; Peichl, M. ; Nilsson, M. ; Zee, S.E.A.T.M. van der; Berendse, F. - \ 2015
Global Change Biology 21 (2015)6. - ISSN 1354-1013 - p. 2309 - 2320.
carbon-dioxide - soil respiration - sphagnum mosses - water-content - solar-radiation - climate-change - precipitation - accumulation - drought - balance
Boreal peatlands store large amounts of carbon, reflecting their important role in the global carbon cycle. The short-term exchange and the long-term storage of atmospheric carbon dioxide (CO2) in these ecosystems are closely associated with the permanently wet surface conditions and are susceptible to drought. Especially, the single most important peat forming plant genus, Sphagnum, depends heavily on surface wetness for its primary production. Changes in rainfall patterns are expected to affect surface wetness, but how this transient rewetting affects net ecosystem exchange of CO2 (NEE) remains unknown. This study explores how the timing and characteristics of rain events during photosynthetic active periods, that is daytime, affect peatland NEE and whether rain event associated changes in environmental conditions modify this response (e.g. water table, radiation, vapour pressure deficit, temperature).
Indicators used in livestock to assess unconsciousness after stunning: a review
Verhoeven, M.T.W. ; Gerritzen, M.A. ; Hellebrekers, L.J. ; Kemp, B. - \ 2015
Animal 9 (2015)2. - ISSN 1751-7311 - p. 320 - 330.
somatosensory-evoked-potentials - penetrating captive bolt - spontaneous electroencephalogram - carbon-dioxide - welfare implications - brain-damage - slaughter - sheep - pigs - cattle
Assessing unconsciousness is important to safeguard animal welfare shortly after stunning at the slaughter plant. Indicators that can be visually evaluated are most often used when assessing unconsciousness, as they can be easily applied in slaughter plants. These indicators include reflexes originating from the brain stem (e.g. eye reflexes) or from the spinal cord (e.g. pedal reflex) and behavioural indicators such as loss of posture, vocalisations and rhythmic breathing. When physically stunning an animal, for example, captive bolt, most important indicators looked at are posture, righting reflex, rhythmic breathing and the corneal or palpebral reflex that should all be absent if the animal is unconscious. Spinal reflexes are difficult as a measure of unconsciousness with this type of stunning, as they may occur more vigorous. For stunning methods that do not physically destroy the brain, for example, electrical and gas stunning, most important indicators looked at are posture, righting reflex, natural blinking response, rhythmic breathing, vocalisations and focused eye movement that should all be absent if the animal is unconscious. Brain stem reflexes such as the cornea reflex are difficult as measures of unconsciousness in electrically stunned animals, as they may reflect residual brain stem activity and not necessarily consciousness. Under commercial conditions, none of the indicators mentioned above should be used as a single indicator to determine unconsciousness after stunning. Multiple indicators should be used to determine unconsciousness and sufficient time should be left for the animal to die following exsanguination before starting invasive dressing procedures such as scalding or skinning. The recording and subsequent assessment of brain activity, as presented in an electroencephalogram (EEG), is considered the most objective way to assess unconsciousness compared with reflexes and behavioural indicators, but is only applied in experimental set-ups. Studies performed in an experimental set-up have often looked at either the EEG or reflexes and behavioural indicators and there is a scarcity of studies that correlate these different readout parameters. It is recommended to study these correlations in more detail to investigate the validity of reflexes and behavioural indicators and to accurately determine the point in time at which the animal loses consciousness.
Forest resilience and tipping points at different spatio-temporal scales: approaches and challenges
Reyer, C.P.O. ; Brouwers, N. ; Rammig, A. ; Brook, B.W. ; Holmgren, M. ; Villela, D.M. - \ 2015
Journal of Ecology 103 (2015)1. - ISSN 0022-0477 - p. 5 - 15.
global vegetation model - climate-change impacts - amazon rain-forest - carbon-dioxide - elevated co2 - tree mortality - boreal forest - regime shifts - primary productivity - critical transitions
1. Anthropogenic global change compromises forest resilience, with profound impacts to ecosystem functions and services. This synthesis paper reflects on the current understanding of forest resilience and potential tipping points under environmental change and explores challenges to assessing responses using experiments, observations and models. 2. Forests are changing over a wide range of spatio-temporal scales, but it is often unclear whether these changes reduce resilience or represent a tipping point. Tipping points may arise from interactions across scales, as processes such as climate change, land-use change, invasive species or deforestation gradually erode resilience and increase vulnerability to extreme events. Studies covering interactions across different spatio-temporal scales are needed to further our understanding. 3. Combinations of experiments, observations and process-based models could improve our ability to project forest resilience and tipping points under global change. We discuss uncertainties in changing CO2 concentration and quantifying tree mortality as examples. 4. Synthesis. As forests change at various scales, it is increasingly important to understand whether and how such changes lead to reduced resilience and potential tipping points. Understanding the mechanisms underlying forest resilience and tipping points would help in assessing risks to ecosystems and presents opportunities for ecosystem restoration and sustainable forest management.
Uncertainties in predicting rice yield by current crop models under a wide range of climatic conditions
Li, T. ; Hasegawa, T. ; Yin, X. ; Zhu, Y. ; Boote, K. ; Adam, M. ; Bregaglio, S. ; Buis, S. ; Confalonieri, R. ; Fumoto, T. ; Gaydon, D. ; Marcaida III, M. ; Nakagawa, H. ; Oriol, P. ; Ruane, A.C. ; Ruget, F. ; Singh, B. ; Singh, U. ; Tang, L. ; Yoshida, H. ; Zhang, Z. ; Bouman, B. - \ 2015
Global Change Biology 21 (2015)3. - ISSN 1354-1013 - p. 1328 - 1341.
air co2 enrichment - high-temperature stress - elevated co2 - spikelet fertility - night temperature - carbon-dioxide - growth - sterility - face - productivity
Predicting rice (Oryza sativa) productivity under future climates is important for global food security. Ecophysiological crop models in combination with climate model outputs are commonly used in yield prediction, but uncertainties associated with crop models remain largely unquantified. We evaluated 13 rice models against multi-year experimental yield data at four sites with diverse climatic conditions in Asia and examined whether different modeling approaches on major physiological processes attribute to the uncertainties of prediction to field measured yields and to the uncertainties of sensitivity to changes in temperature and CO2 concentration [CO2]. We also examined whether a use of an ensemble of crop models can reduce the uncertainties. Individual models did not consistently reproduce both experimental and regional yields well, and uncertainty was larger at the warmest and coolest sites. The variation in yield projections was larger among crop models than variation resulting from 16 global climate model-based scenarios. However, the mean of predictions of all crop models reproduced experimental data, with an uncertainty of less than 10% of measured yields. Using an ensemble of eight models calibrated only for phenology or five models calibrated in detail resulted in the uncertainty equivalent to that of the measured yield in well-controlled agronomic field experiments. Sensitivity analysis indicates the necessity to improve the accuracy in predicting both biomass and harvest index in response to increasing [CO2] and temperature.
No growth stimulation of tropical trees by 150 years of CO2 fertilization but water-use efficiency increased
Sleen, J.P. van der; Groenendijk, P. ; Vlam, M. ; Anten, N.P.R. ; Boom, A. ; Bongers, F. ; Pons, T.L. ; Terburg, G. ; Zuidema, P.A. - \ 2015
Nature geoscience 8 (2015). - ISSN 1752-0894 - p. 24 - 28.
rising atmospheric co2 - carbon-dioxide - climate-change - elevated co2 - forest trees - responses - ecosystems - vegetation - feedbacks - lessons
The biomass of undisturbed tropical forests has likely increased in the past few decades (1, 2), probably as a result of accelerated tree growth. Higher CO2 levels are expected to raise plant photosynthetic rates (3) and enhance water-use efficiency (4), that is, the ratio of carbon assimilation through photosynthesis to water loss through transpiration. However, there is no evidence that these physiological responses do indeed stimulate tree growth in tropical forests. Here we present measurements of stable carbon isotopes and growth rings in the wood of 1,100 trees from Bolivia, Cameroon and Thailand. Measurements of carbon isotope fractions in the wood indicate that intrinsic water-use efficiency in both understorey and canopy trees increased by 30–35% over the past 150 years as atmospheric CO2 concentrations increased. However, we found no evidence for the suggested concurrent acceleration of individual tree growth when analysing the width of growth rings. We conclude that the widespread assumption of a CO2-induced stimulation of tropical tree growth may not be valid.
Analysis of the mechanisms of bioelectrochemical methane production by mixed cultures
Eerten-Jansen, M.C.A.A. van; Jansen, N.C. ; Plugge, C.M. ; Wilde, V. de; Buisman, C.J.N. ; Heijne, A. ter - \ 2015
Journal of Chemical Technology and Biotechnology 90 (2015)5. - ISSN 0268-2575 - p. 963 - 970.
microbial electrolysis cells - fuel-cells - carbon-dioxide - electricity - acetate - co2 - electromethanogenesis - electrosynthesis - performance - generation
BACKGROUND In a methane-producing bioelectrochemical system (BES) microorganisms grow on an electrode and catalyse the conversion of CO2 and electricity into methane. Theoretically, methane can be produced bioelectrochemically from CO2 via direct electron transfer or indirectly via hydrogen, acetate or formate. Understanding the electron transfer mechanisms could give insight into methods to steer the process towards higher rate. RESULTS In this study, the electron transfer mechanisms of bioelectrochemical methane production by mixed cultures were investigated. At a cathode potential of -0.7¿V vs. normal hydrogen electrode (NHE), average current density was 2.9 A m-2 cathode and average methane production rate was 1.8 mole e- eq m-2 cathode per day (5.2¿L CH4 m-2 cathode per day). Methane was primarily produced indirectly via hydrogen and acetate. Methods to steer towards bioelectrochemical hydrogen and acetate production to further improve the performance of a methane-producing BES are discussed. CONCLUSION At cathode potentials equal to or lower than -0.7¿V vs. NHE and using mixed cultures, methane was primarily produced indirectly via hydrogen and acetate. (Bio)electrochemical hydrogen and acetate production rate could be increased by optimizing the cathode design and by enriching the microbial community. Consequently, the production rate of CO2-neutral methane in a BES could be increased. © 2014 Society of Chemical Industry
Modelling forest dynamics along climate gradients in Bolivia
Seiler, C. ; Hutjes, R.W.A. ; Kruijt, B. ; Quispe, J. ; Añez, S. ; Arora, V.K. ; Melton, J.R. ; Hickler, T. ; Kabat, P. - \ 2014
Journal of Geophysical Research: Biogeosciences 119 (2014)5. - ISSN 2169-8953 - p. 758 - 775.
global vegetation model - tropical forest - terrestrial biosphere - carbon-dioxide - rain-forest - biomass - productivity - variability - drought - dieback
Dynamic vegetation models have been used to assess the resilience of tropical forests to climate change, but the global application of these modeling experiments often misrepresents carbon dynamics at a regional level, limiting the validity of future projections. Here a dynamic vegetation model (Lund Potsdam Jena General Ecosystem Simulator) was adapted to simulate present-day potential vegetation as a baseline for climate change impact assessments in the evergreen and deciduous forests of Bolivia. Results were compared to biomass measurements (819 plots) and remote sensing data. Using regional parameter values for allometric relations, specific leaf area, wood density, and disturbance interval, a realistic transition from the evergreen Amazon to the deciduous dry forest was simulated. This transition coincided with threshold values for precipitation (1400 mm yr-1) and water deficit (i.e., potential evapotranspiration minus precipitation) (-830 mm yr-1), beyond which leaf abscission became a competitive advantage. Significant correlations were found between modeled and observed values of seasonal leaf abscission (R2 = 0.6, p
Net CO2 surface emissions at Bern, Switzerland inferred from ambient observations of CO2, d(O2/N2), and 222Rn using a customized radon tracer inversion
Laan, S. van der; Laan-Luijkx, I.T. van der; Zimmermann, L. ; Conen, F. ; Leuenberger, M. - \ 2014
Journal of Geophysical Research: Atmospheres 119 (2014)3. - ISSN 2169-897X - p. 1580 - 1591.
carbon-dioxide - netherlands - methane - rn-222 - air
The 222Radon tracer method is a powerful tool to estimate local and regional surface emissions of, e.g., greenhouse gases. In this paper we demonstrate that in practice, the method as it is commonly used, produces inaccurate results in case of nonhomogeneously spread emission sources, and we propose a different approach to account for this. We have applied the new methodology to ambient observations of CO2 and 222Radon to estimate CO2 surface emissions for the city of Bern, Switzerland. Furthermore, by utilizing combined measurements of CO2 and d(O2/N2) we obtain valuable information about the spatial and temporal variability of the main emission sources. Mean net CO2 emissions based on 2 years of observations are estimated at (11.2¿±¿2.9) kt km-2 a-1. Oxidative ratios indicate a significant influence from the regional biosphere in summer/spring and fossil fuel combustion processes in winter/autumn. Our data indicate that the emissions from fossil fuels are, to a large degree, related to the combustion of natural gas which is used for heating purposes.
Starch hydrolysis in autogenerative high pressure digestion: Gelatinisation and saccharification as rate limiting steps
Lindeboom, R.E.F. ; Ding, L. ; Weijma, J. ; Plugge, C.M. ; Lier, J.B. van - \ 2014
Biomass and Bioenergy 71 (2014). - ISSN 0961-9534 - p. 256 - 265.
amylolytic enzymes - carbon-dioxide - anaerobic-digestion - kinetics - biogas - temperature - bacterium - reactors - amylase
Autogenerative high pressure digestion (AHPD) provides an integrated biogas upgrading technology, capable of producing biogas with a CH4 content exceeding 95% at pressures up to 90 bar. Hydrolysis is generally regarded as the rate-limiting step in the anaerobic digestion of complex organic matter, governing the volatile fatty acid (VFA) production rate for subsequent conversion to methane. Starch hydrolysis rates in AHPD systems were studied and the potential risk for VFA accumulation was assessed. Under the anticipated practical moderate pressure conditions at 30 °C, experimental CH4-content of the biogas improved from 49 to 73 ± 2% at atmospheric and elevated pressure, respectively. Furthermore, no significant effect of pressure on the hydrolysis was found. Like under atmospheric pressure, gelatinisation was the rate-limiting step for particulate starch (0.05 d-1) and saccharification for gelatinised starch (0.1 d-1). Because no effect was observed on starch, an effect on the hydrolysis rate of more complex organic matter like (ligno-)cellulose is also not anticipated.
Mud, muddle and models in the knowledge value-chain to action on tropical peatland conservation
Noordwijk, M. van; Matthews, R.B. ; Agus, F. ; Farmer, J. ; Verchot, L. ; Hergoualc’h, K. ; Persch, S. ; Tata, H.L. ; Lusiana, B. ; Widayati, A. ; Dewi, S. - \ 2014
Mitigation and Adaptation Strategies for Global Change 19 (2014)6. - ISSN 1381-2386 - p. 887 - 905.
greenhouse-gas emissions - hydrological restoration - central kalimantan - carbon-dioxide - climate-change - decomposition - strategies - management - indonesia - soils
Tropical peatlands are known not only for their high, area-based, carbon emissions in response to land-use change but also as hot spots of debate about associated data uncertainties. Perspectives are still evolving on factors underlying the variability and uncertainty. Debate includes the ways of reducing emissions through rewetting, reforestation and agroforestry. A knowledge value-chain that is long and complex links (a) fundamental understanding of peat and peatland processes leading to sciencebased quantification and default values, (b) willingness and (c) ability to act towards emission reduction, and ultimately (d) to local, national and global actions that effectively provide rules, incentives and motivation to conserve peat and reduce emissions. We discuss this value chain, its stakeholders and issues that still remain partially unresolved.We conclude that, to shorten the denial and conspiracy-theory stages of debate that otherwise slow down steps B and C, networks of international and national scientists have to be involved at the early stage of identifying policysensitive environmental issues. Models span part of the knowledge value-chain but transition of analysis units requires specific attention, from soil volumes through area and commodity flows to opportunities for reductions. While drainage of peatlands triggers landscape-scale increases in emissions, factors beyond drainage depth, including nutrient supply, may have a major influence on decomposition rates. Attempts to disentangle the contributions of plant and peat-based respiration in surface flux measurements involve assumptions that cannot be easily verified in comparisons between land uses. With progress on A leading to new internationally accepted defaults and with resistance on step B reduced, the reality of C and lack of working solutions for D is currently constraining further progress.
Stomatal malfunctioning under low VPD conditions: induced by alterations in stomatal morphology and leaf anatomy or in the ABA signaling?
Ali Niaei Fard, S. ; Malcolm Matamoros, P. ; Meeteren, U. van - \ 2014
Physiologia Plantarum 152 (2014)4. - ISSN 0031-9317 - p. 688 - 699.
relative-air-humidity - abscisic-acid - tradescantia-virginiana - water-loss - in-vitro - response characteristics - carbon-dioxide - growth - plants - arabidopsis
Exposing plants to low VPD reduces leaf capacity to maintain adequate water status thereafter. To find the impact of VPD on functioning of stomata, stomatal morphology and leaf anatomy, fava bean plants were grown at low (L, 0.23 kPa) or moderate (M, 1.17 kPa) VPDs and some plants that developed their leaves at moderate VPD were then transferred for 4 days to low VPD (M[RIGHTWARDS ARROW]L). Part of the M[RIGHTWARDS ARROW]L-plants were sprayed with ABA (abscisic acid) during exposure to L. L-plants showed bigger stomata, larger pore area, thinner leaves and less spongy cells compared with M-plants. Stomatal morphology (except aperture) and leaf anatomy of the M[RIGHTWARDS ARROW]L-plants were almost similar to the M-plants, while their transpiration rate and stomatal conductance were identical to that of L-plants. The stomatal response to ABA was lost in L-plants, but also after 1-day exposure of M-plants to low VPD. The level of foliar ABA sharply decreased within 1-day exposure to L, while the level of ABA-GE (ABA-glucose ester) was not affected. Spraying ABA during the exposure to L prevented loss of stomatal closing response thereafter. The effect of low VPD was largely depending on exposure time: the stomatal responsiveness to ABA was lost after 1-day exposure to low VPD, while the responsiveness to desiccation was gradually lost during 4-day exposure to low VPD. Leaf anatomical and stomatal morphological alterations due to low VPD were not the main cause of loss of stomatal closure response to closing stimuli.
Evaluation of textile substrates for dispensing synthetic attractants for malaria mosquitoes
Mweresa, C.K. ; Mukabana, W.R. ; Omusula, P. ; Otieno, B. ; Gheysens, G. ; Takken, W. ; Loon, J.J.A. van - \ 2014
Parasites & Vectors 7 (2014). - ISSN 1756-3305 - 10 p.
vector anopheles-gambiae - sensu-stricto diptera - baited entry traps - western kenya - semifield conditions - carbon-dioxide - host - arabiensis - behavior - nets
Background The full-scale impact of odour-baited technology on the surveillance, sampling and control of vectors of infectious diseases is partly limited by the lack of methods for the efficient and sustainable dispensing of attractants. In this study we investigated whether locally-available and commonly used textiles are efficient substrates for the release of synthetic odorant blends attracting malaria mosquitoes. Methods The relative efficacy of (a) polyester, (b) cotton, (c) cellulose¿+¿polyacrylate, and (d) nylon textiles as substrates for dispensing a synthetic odour blend (Ifakara blend 1(IB1)) that attracts malaria mosquitoes was evaluated in western Kenya. The study was conducted through completely randomized Latin square experimental designs under semi-field and field conditions. Results Traps charged with IB1-impregnated polyester, cotton and cellulose¿+¿polyacrylate materials caught significantly more female Anopheles gambiae sensu stricto (semi-field conditions) and An. gambiae sensu lato (field conditions) mosquitoes than IB1-treated nylon (P¿=¿0.001). The IB1-impregnated cellulose¿+¿polyacrylate material was the most attractive to female An. funestus mosquitoes compared to all other dispensing textile substrates (P¿
Development and optimization of the Suna trap as a tool for mosquito monitoring and control
Hiscox, A.F. ; Otieno, B. ; Kibet, A. ; Mweresa, C.K. ; Omusula, P. ; Geier, M. ; Rose, A. ; Mukabana, W.R. ; Takken, W. - \ 2014
Malaria Journal 13 (2014). - ISSN 1475-2875 - 14 p.
human-landing catches - cdc light-trap - anopheles-gambiae - carbon-dioxide - malaria transmission - field-evaluation - diptera-culicidae - equatorial-guinea - vector control - western kenya
Background Monitoring of malaria vector populations provides information about disease transmission risk, as well as measures of the effectiveness of vector control. The Suna trap is introduced and evaluated with regard to its potential as a new, standardized, odour-baited tool for mosquito monitoring and control. Methods Dual-choice experiments with female Anopheles gambiae sensu lato in a laboratory room and semi-field enclosure, were used to compare catch rates of odour-baited Suna traps and MM-X traps. The relative performance of the Suna trap, CDC light trap and MM-X trap as monitoring tools was assessed inside a human-occupied experimental hut in a semi-field enclosure. Use of the Suna trap as a tool to prevent mosquito house entry was also evaluated in the semi-field enclosure. The optimal hanging height of Suna traps was determined by placing traps at heights ranging from 15 to 105 cm above ground outside houses in western Kenya. Results In the laboratory the mean proportion of An. gambiae s.l. caught in the Suna trap was 3.2 times greater than the MM-X trap (P <0.001), but the traps performed equally in semi-field conditions (P = 0.615). As a monitoring tool , the Suna trap outperformed an unlit CDC light trap (P <0.001), but trap performance was equal when the CDC light trap was illuminated (P = 0.127). Suspending a Suna trap outside an experimental hut reduced entry rates by 32.8% (P <0.001). Under field conditions, suspending the trap at 30 cm above ground resulted in the greatest catch sizes (mean 25.8 An. gambiae s.l. per trap night). Conclusions The performance of the Suna trap equals that of the CDC light trap and MM-X trap when used to sample An. gambiae inside a human-occupied house under semi-field conditions. The trap is effective in sampling mosquitoes outside houses in the field, and the use of a synthetic blend of attractants negates the requirement of a human bait. Hanging a Suna trap outside a house can reduce An. gambiae house entry and its use as a novel tool for reducing malaria transmission risk will be evaluated in peri-domestic settings in sub-Saharan Africa.
A multi-year methane inversion using SCIAMACHY, accounting for systematic errors using TCCON measurements
Houweling, S. ; Krol, M.C. ; Bergamaschi, P. ; Frankenberg, C. ; Dlugokencky, E.J. ; Morino, I. - \ 2014
Atmospheric Chemistry and Physics 14 (2014). - ISSN 1680-7316 - p. 3991 - 4012.
column observing network - atmospheric methane - carbon-dioxide - tropospheric methane - lower stratosphere - data assimilation - transport model - emissions - ch4 - gosat
This study investigates the use of total column CH4 (XCH4) retrievals from the SCIAMACHY satellite instrument for quantifying large-scale emissions of methane. A unique data set from SCIAMACHY is available spanning almost a decade of measurements, covering a period when the global CH4 growth rate showed a marked transition from stable to increasing mixing ratios. The TM5 4DVAR inverse modelling system has been used to infer CH4 emissions from a combination of satellite and surface measurements for the period 2003–2010. In contrast to earlier inverse modelling studies, the SCIAMACHY retrievals have been corrected for systematic errors using the TCCON network of ground-based Fourier transform spectrometers. The aim is to further investigate the role of bias correction of satellite data in inversions. Methods for bias correction are discussed, and the sensitivity of the optimized emissions to alternative bias correction functions is quantified. It is found that the use of SCIAMACHY retrievals in TM5 4DVAR increases the estimated inter-annual variability of large-scale fluxes by 22% compared with the use of only surface observations. The difference in global methane emissions between 2-year periods before and after July 2006 is estimated at 27–35 Tg yr-1. The use of SCIAMACHY retrievals causes a shift in the emissions from the extra-tropics to the tropics of 50 ± 25 Tg yr-1. The large uncertainty in this value arises from the uncertainty in the bias correction functions. Using measurements from the HIPPO and BARCA aircraft campaigns, we show that systematic errors in the SCIAMACHY measurements are a main factor limiting the performance of the inversions. To further constrain tropical emissions of methane using current and future satellite missions, extended validation capabilities in the tropics are of critical importance.
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